Intravascular catheters, such as catheters for advancement into the arterial system around the heart, are presently in wide clinical use both for angiography and angioplasty (PTCA). As is well known, the catheter must be made of a flexible material which, nevertheless, exhibits a certain stiffness so that the catheter may be advanced through the various twists and turns of the arterial system to bring an angioplasty balloon or other clot opening device, for example, to the desired site of arterial occlusion. Also, while the plastic body of the catheter must exhibit this desired stiffness and other particular characteristics, the catheter lumen must have a low friction surface so that the catheter can be advanced along a guidewire, and also a guidewire or inner catheter can be advanced through the catheter lumen.
Conventionally, a catheter having a nylon body or a body of polyethylene, polyurethane, poly(ethylene terephthalate) (known as PET) is used, with the catheter lumen having a lubricating coating or containing a preformed polytetrafluoroethylene (PTFE) sleeve. This inner PTFE sleeve provides the desired low friction to the catheter lumen, while the balance of the catheter can provide other desired qualities. However, it has sometimes been found that the presence of the PTFE tubing can make the catheter too stiff, as well as unduly subject to kinking, when the catheter turns a sharp corner in the arterial system of the patient in which it is used.
PTFE is of course a stiff plastic, and this has to be accommodated for by reducing the thickness of the outer catheter layer by an amount that may cause other characteristics of the catheter to be less than optimum. Also, the PTFE of course does not bond in any significant way to the nylon or PET outer catheter layer. This provides an added possible disadvantage that the PTFE tubing may shift with respect to the outer catheter layer and slide out of the lumen to a certain extent. As is well known, PTFE bonds only with great difficulty to most other plastic materials.
If it were desired to replace the inner PTFE tubing in conventional catheters with another low friction plastic such as a high density polyethylene, this material also is incompatible with nylon, for example, and does not form a significant bond with nylon upon coextrusion of tubing with a nylon outer layer and a high density polyethylene inner layer. Such layers also can slip in their relative position because of the essential absence of a bond, even after coextrusion.
As another prior art expedient, the interior of a catheter is coated with a friction reducing material such as a silicone in liquid form, which is then dried. Such processes are particularly difficult with small diameter intravascular catheters. Also, silicone resins and the like which are used for such coating lack the best low friction characteristics to facilitate advancement of such catheters along a guidewire.
In accordance with this invention, a catheter is provided having tubing with inner and outer tubular layers which are bonded to each other for firm retention and ease of manufacture. The manufacturing may be simply by coextrusion, while obtaining the desired bond and other desired characteristics of the respective inner and outer catheter layers to optimize overall catheter performance.